1. Field of the Invention
This invention relates to computer systems and, more specifically, to a system and method which will support ISA-derived Direct Memory Access (DMA) Input/Output (I/O) devices without requiring an Industry Standard Architecture (ISA) bus and, if an ISA bus is provided, the system and method will support DMA I/O devices and ISA Masters on the ISA bus.
2. Description of the Prior Art
The Peripheral Component Interconnect (PCI) bus does not provide any direct support for DMA devices ISA or otherwise. This is a problem for many types of machines, particularly International Business Machines (IBM) Personal Computer (PC) AT compatible machines, which use a specific DMA programming model. In past IBM PC/AT designs, DMA I/O devices were only supported if the DMA devices were connected to an ISA bus. The ISA bus provided direct support for DMA I/O devices through a pair of signal lines DRQ/DACK#. However, these signal lines were not easily useable by DMA devices which do not attach to the ISA bus but require software compatibility.
Therefore, a need existed to provide a system and method for supporting DMA I/O devices that are coupled to a PCI bus. This will allow IBM PC/AT machines to support DMA I/O devices without requiring an ISA bus. However, if an ISA bus is provided, the system and method will still support DMA I/O devices and ISA Masters on the ISA bus.